Northcombe Water Treatment Works to Prewley Water Treatment Works

Due to climate change and increasing populations the demand for water resources is growing across southern England and in North Devon. To enhance water supply resilience in the regions two new water transfer mains between Northcombe Water Treatment Works and Prewley Water Treatment Works (WTW) were implemented by South West Water. These mains will ensure an all year round reliable supply of drinking water, transferring water across the network to locations where it is needed.

Working for our client, Galliford Try, Pell Frischmann undertook the design of the two new water transfer mains. The project involved adding 10 km of new raw water and 10 km of treated water pipelines connecting Prewley WTW and Northcombe WTW, to provide strategic links between these key water supply and treatment centres.

What we did

Pell Frischmann is pleased to have delivered detailed designs for the two pipelines, including a treated water pumping station, inlet, outlet and permanent connections at the WTW sites.

Specialist support was provided by subcontractors for pipeline surge analysis. The project involved cross country pipelines and involved multiple lengths of directional drilling beneath busy roads and rivers, effectively avoiding several strategic service crossings.

The Prewley to Northcombe pipeline is designed to transfer raw water flow by gravity, and potable water in the opposite direction with the assistance of a new treated water pumping station.

Outcomes

The scheme is designed to enhance the resilience of the water supply in North Devon, ensuring reliable water supply during extended periods of low rainfall or drought. Additionally, it will facilitate the rationalisation of WTWs in North Devon, reducing dependency on individual treatment works and strengthening overall system reliability. The project will create a more balanced and adaptable water infrastructure, improving operational efficiency and enhancing water quality across the network.

We optimised the pipeline diameters, and working with Galliford Try and South West Water, changed the pipeline route to facilitate construction works and to lessen the impact on landowners.

Construction was successfully completed in 2025.